The DePriester Charts for the homologous series of light hydrocarbons can serve as a basis with approximate validity for simple calculations of VLE situations. Originally there were charts prepared to make use of these definitions. Used by permission DePnester, C.L., The American Institute of Chemical Engineers, Chemical Eng. DePriester Charts K-Values of light hydrocarbon systems, generalized oorreiations, low-temperature range. Next, calculate the relative volatility of the feed stream, defined by Equation 6.27.18, for each component relative to the heavy key component. Bubble and dew points could also be calculated using K-values from the DePriester charts and by using the calculation procedures given in Chapter 3. The K-values of the feed are listed in Table 6.7.1.
The bubble point of the feed at 400 psia (27.6 bar) and at the feed composition, calculated using ASPEN, is 86.5 ☏ (130 ☌). The relative volatility depends on temperature and pressure. To obtain the composition of the top and bottom products, first calculate the relative volatility of each component using the conditions of the feed as a first guess. Įquilibrium constants were taken from the Depriester charts (Chapter 8). Take the equilibrium data from the Depriester charts given in Chapter 8. Calculate the flow and composition of the liquid and vapour phases. Ī feed to a column has the composition given in the table below, and is at a pressure of 14 bar and a temperature of 60☌. The DePriester charts check this quite well (see Figures 8-4A and B, and Figure 8-3D). For n-pentane at convergence pressure of 3,000 psia (nearest chart) the K-value reads 0.19. įor a temperature of 100☏, the convergence pressure is approximately 2,500 psia (dotted line) for the pseudo system methane-n-pentane (see Figure 8-3C). Regression equations and coefficients for various versions of the GPA convergence-pressure charts are available from the GPA. The widespread availabihty and utihzation of digital computers for distillation calculations have given impetus to the development of analytical expressions for i regression equation and accompanying regression coefficients that represent the DePriester charts of Fig. It is analogous to the critical point for a pure component in the sense that the two. An alternative measure of composition is the convergence pressure of the system, which is defined as that pressure at which the Kvalues for aU the components in an isothermal mixture converge to unity.
The Kellogg and DePriester charts and their subsequent extensions and generahzations use the molar average boiling points of the liquid and vapor phases to represent the composition effect. SI versions of these charts have been developed by Dadyburjor. For K as a function of T and P only, the DePriester charts provide good starting values for the iteration. One cannot calculate K values until phase compositions are known, and those cannot be known until the K values are available to calculate them. Ī trial-and- error procedure is required with any K-value correlation that takes into account the effect of composition. The Kellogg charts, and hence the DePriester charts, are based primarily on the Benedict-Webb-Rubin equation of state, which can represent both the liquid and the vapor phases and can predict K values quite accurately when the equation constants are available for the components in question. These charts are a simplification of the Kellogg charts and include additional experimental data. The easiest to use are the DePriester charts, which cover 12 hydrocarbons (methane, ethylene, ethane, propylene, propane, isobutane, isobutylene, /i-butane, isopentane, /1-pentane, /i-hexane, and /i-heptane). For example, several major graphical i light-hydrocarbon systems. However, for mixtures of compounds of similar molecular structure and size, the K value depends mainly on temperature and pressure. 4, the i complex function of temperature, pressure, and equilibrium vapor- and hquid-phase compositions.
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